The field of the present invention is dewatering processes and apparatus for recovering water from waste drilling fluid for concurrent reutilization with an active drilling operation.
During the course of a drilling operation large quantities of water are consumed and must be continuously supplied so as not to slow down the drilling process. Much of the water consumed in a drilling operation is utilized to dilute drilling mud which serves to lubricate and cool the drill bit as well as circulate cuttings from the wellbore to the surface. As the cuttings build up in the drilling mud, the mud thickens and must be diluted with water. Consequently, the volume of drilling mud increases to a point where the excess mud and water contained therein must be disposed of as waste. The conventional practice is to dump the excess mud in a reserve pit or "sump" at the wellsite.
Water is also utilized at the wellsite for many purposes including washing off the drilling equipment. Accordingly, as the water collects around the drillsite it becomes contaminated with various materials and must be disposed of as contaminated water. A typical procedure is to transfer the contaminated water to the reserve pit or "sump" wherein it is mixed with the excess mud and later hauled away to a disposal site.
The combination of new environmental regulations, transportation fees, disposal site fees and associated costs make the disposal of waste drilling mud and contaminated water quite expensive. Similarly, it becomes quite costly to have a continuous supply of clean water trucked into the wellsite. This is especially true for wells that are often drilled in remote, dry areas that do not have access to large amounts of water.
A variety of techniques have been developed for dewatering mud waste pits and for purifying contaminated water thereby reducing the volume of waste and, hence, the waste disposal costs. The thrust of these techniques is to clean up existing sumps and holding tanks containing drilling mud and/or contaminated waste water. For example, U.S. Pat. No. 4,536,293 to Babineaux, III discloses a method for purifying waste water from a drilling operation utilizing a flocculation, aeration and sedimentation process. However, this method is incapable of dewatering waste drilling mud in a timely manner because of the drilling mud's high solids and/or clay content. U.S. Pat. No. 4,395,338 to Rowton discloses a method for dewatering a reserve pit through a boiling process. However, no provisions are made for recovering or reusing the water once it is separated from the waste drilling mud. Some techniques have even been developed to recover water that may be reused on some other drilling project. For example, U.S. Pat. No. 4,366,063 to O'Connor discloses a method for removing reusable water from waste drilling mud by passing the water through a filtering and absorbing means and then subjecting the water to reverse osmosis. However, this method is also incapable of clarifying large volumes of high solids and/or clay content fluids in a timely and economical manner. Also, articles have been published (e.g. Wojtanowicz, A. K., Society of Petroleum Engineers of AIME, p. 417-428, IADC/SPE/16098, March 1987; Nordquist, D. G. et al., IADC/SPE Drilling Conference, IADC/SPE #17246 February 1988) disclosing dewatering studies that have incorporated a flocculation process and centrifuge capable of dewatering waste drilling mud.
However, none of the methods discussed above discloses a means for solving the problem solved by the invention described herein.